We present the design of a compact synchrotron light source for the production of EUV radiation for metrology applications in the semiconductor industry. Stable, high brightness EUV light sources are of great potential interest for this industry. The recent availability of highly reflective mirrors at 13.5 nm wavelength makes EUV lithography a strong candidate for future generation semiconductor manufacture. Our design is based on a storage ring lattice employing design principles similar to those used in the new family of diffraction limited synchrotron radiation sources. The 430 MeV storage ring of circumference 25.8 m would have an emittance of ~ 6 nm-rad. The required EUV wavelength is obtained using a short period (16 mm) undulator.

The horizontal emittance of a storage ring beam can be reduced below the theoretical minimum of a given magnet structure if a variation of the longitudinal field is introduced in the bending magnets. The optimum longitudinal field variation for the generation of the lowest emittance has been calculated numerically – and analytically for different classes of simple functions: exponential-, power-, hyperbolic- and step-function. Constraints have been introduced for the maximum field and the minimum beta function in the magnet. The distribution of the deflection angles to the different magnet types has been optimized. The optimization results have been applied to an exemplary design of a lattice for a light source with limited circumference as for instance the Swiss Light Source.

MedAustron is the Austrian ion therapy and research centre, presently under construction in Wiener Neustadt, Austria. The facility is based on a synchrotron which will deliver proton beams with kinetic energies up to 250 MeV and carbon ion beams up to 400 MeV/nucleon for clinical applications. In addition to the clinical applications, the accelerator will provide beams for nonclinical research in the fields of medical radiation physics, radiation biology and experimental physics with a proton energy range extended beyond medical requirements to 800MeV. An overview is given on the historical development of the project. The main design features of the accelerator facilities and medical facilities are presented and the actual status of the project is summarized.

Experimental and simulation results of an electron gun test facility, based on pulsed diode acceleration followed by a two-cell rf cavity at 1.5 GHz, are presented here. The main features of this diode-rf combination are: a high peak gradient in the diode (up to 100 MV/m) obtained without breakdown conditioning, a cathode shape providing an electrostatic focusing, and an in-vacuum pulsed solenoid to focus the electron beam between the diode and the rf cavity. Although the test stand was initially developed for testing field emitter arrays cathodes, it became also interesting to explore the limits of this electron gun with metallic photocathodes illuminated by laser pulses. The ultimate goal of this test facility is to fulfill the requirements of the SwissFEL project of Paul Scherrer Institute [B.D. Patterson et al., New J. Phys. 12, 035012 (2010)]; a projected normalized emittance below 0.4 mu m for a charge of 200 pC and a bunch length of less than 10 ps (rms). A normalized projected emittance of 0.23 mu m with 13 pC has been measured at 5 MeV using a Gaussian laser longitudinal intensity distribution on the photocathode. Good agreements with simulations have been obtained for different electron bunch charge and diode geometries. Emittance measurements at a bunch charge below 1 pC were performed for different laser spot sizes in agreement with intrinsic emittance theory [e.g. 0.54 mu m/mm of laser spot size (rms) for Cu at 274 nm]. Finally, a projected emittance of 1.25 + / - 0.2 mu m was measured with 200 pC and 100 MV/m diode gradient.

The authors studied the photoemission from molybdenum nanotip arrays with controlled apex curvatures by photoelectron microscopy and spectroscopy excited by 10 ps visible laser pulses under dc electric field. While two-photon photoemission microscopy demonstrates the enhancement of photoabsorption at the sharp tip apex, spatially resolved analysis of the photoelectron energy revealed anomalous energy distribution that is ascribed to the dc field enhancement and resultant barrier reduction at the tip apex. The results show the applicability of photoelectron microscopy and spectroscopy to study the distribution of dc and optical electric field enhancement in field-emitter arrays.

The authors proposed a method to fabricate field emitter arrays with uniform apex diameters in tens of nanometer scale based on the molding technique and apply it to fabricate molybdenum field emitter arrays. Apex diameter equal to 23±5nm was observed in a 6×6 tip array by high-resolution scanning electron microscope. They also studied the field-emission characteristics in devices with gate electrodes fabricated on top of the arrays by a self-aligned process. In single-gate devices, emission current of up to 20μA per tip with negligible gate leak current was observed. The gate-fabrication process was extended to fabricate double-gated emitters. Further optimization of the fabrication process for higher emission current, together with metallurgical and lithographic methods, is discussed.

Since 2003, PSI has been investigating an advanced Low Emittance Gun (LEG) based XFEL facility to supply coherent, ultra-bright, and ultra-short photon beams covering the wavelengths from 0.1 nm to 10 nm. To build the facility within a length of 800 m, challenging beam parameters are required at the entrance of the undulators. For the first two FEL beamlines (FEL1 and FEL2), the required normalized slice emittance, slice energy spread, and peak current are about 0.2 μm, 0.6 MeV, and 1.5 kA respectively. However, the required beam parameters for the third FEL beamline (FEL3), covering 1 nm to 10 nm, are somewhat flexible. Therefore we are developing two different gun technologies. The 1 MV high gradient pulsed diode and field emission based advanced LEG will be used for the first two FEL beamlines, while a CTF3 gun based RF photoinjector will be used for the third FEL beamline. To test these two injector technologies, a 250 MeV injector test facility will be constructed at PSI from 2008. In this paper, we describe beam dynamics for two different injector optimizations of the CTF3 RF gun based injector test facility.

Paul Scherrer Institute (PSI) is presently developing a low-emittance electron source for the PSI-XFEL project. The electron gun consists of an adjustable diode configuration subject to pulses of 250 ns (FWHM) with amplitude up to 500 kV from an air-core transformer-based high-voltage pulser. The facility allows high gradient tests with different cathode configurations and emission processes (pulsed field emission and photo emission). In the first stage, the beamline consists of focusing solenoids followed by an emittance monitor. Selected beam characterization measurements from photo cathode operation driven by a 266 nm UV laser system delivering 4 μJ energy during 6.5 ps (RMS) are presented and compared to the results of 3D particle tracking simulations. INTRODUCTION AND MOTIVATION The goal of the PSI-XFEL project is the realization of an X-ray Free Electron Laser (FEL) operating in the wavelength range between 1 and 100 A and producing up to 10 photons per pulse at a repetition rate of 100 Hz. To keep spatial and financial requirements within reasonable limits, the project foresees a compact design featuring a 6 GeV S-band main linac. This compact layout requires a high-brightness electron beam, which in turn calls for a low-emittance source. The strategy chosen for the PSIXFEL project consists in utilizing a high-voltage pulsed diode providing fast acceleration with a special cathode optimized for low emittance (photo cathode or field emitter array). To evaluate various configurations and materials, a test stand has been set up at PSI consisting of a pulser, a laser system and a diagnostic beamline [1]. Figure 1 gives an overview of the pulser and beamline assembly. An important aspect of the test facility, in particular in view of the further advancement of the PSI-XFEL project, is to improve the understanding of the space charge dominated electron beam by way of simulation. Indeed, one of the objectives of the test facility is the validation of our 3D particle tracking code against observations. In this paper we present a set of measurements taken at the test facility and compare it to the result of a 3D particle simulation. Figure 1: Schematic view of pulser (left) and diagnostic beamline, including the emittance monitor (right).

Illumination of a ZrC needle with short laser pulses (16 ps, 266 nm) while high voltage pulses (-60 kV, 2 ns, 30 Hz) are applied, produces photo-field emitted electron bunches. The electric field is high and varies rapidly over the needle surface so that quantum efficiency (QE) near the apex can be much higher than for a flat photocathode due to the Schottky effect. Up to 150 pC (2.9 A peak current) have been extracted by photo-field emission from a ZrC needle. The effective emitting area has an estimated radius below 50 microm leading to a theoretical intrinsic emittance below 0.05 mm mrad.

The authors explore the impact of femtosecond light pulses on the field-emission properties of single-gate molybdenum field-emitter arrays with nanometer scale tip apex. Despite the small fraction of the emission area, we observed a single-photon photoelectric current from the emitter tips on top of the dc field-emission current under the irradiation of 50fs laser pulses at a wavelength of 800nm with an external quantum efficiency up to ∼2×10−7 and the emitter tip quantum efficiency of ∼10−2. The result indicates that metallic field-emitter arrays are promising for applications that require high-brightness short electron beams.

The reduction of horizontal emittance beyond the conventional limit is pursued by introducing a longitudinal variation of the field in a bending magnet. For a given dipole field, the search for the minimal emittance is formulated analytically under different boundary conditions, starting from the achromat condition, preferred for light source rings. With a dipole field rapidly decaying along the longitudinal position, it is shown that the emittance can be further reduced, essentially by rendering the H function to be out of phase with the third power of the local curvature. Under the minimal emittance condition analytically obtained, the optimal dipole field distribution is searched numerically with a polynomial function, analysing at the same time the mechanism of the emittance reduction. The minimal emittance is argued as a function of the required peak field and the field distribution. Adaptability of longitudinally varying dipole fields in a standard magnet lattice for light sources is also addressed.

A low-emittance and high-brightness electron source is a prerequisite for the successful development of sub-nm wavelength x-ray free electron lasers (XFEL). For that application, a field emitter array (FEA) device equipped with a focusing gate is potentially advantageous over the state-of-the-art photocathode. In the low-emittance gun design of the PSI-XFEL project at the Paul Scherrer Institut, the cathode is assumed to emit above 0.2 nC within 10-40 ps, or -10 A, from an array of total area below 1 mm in diameter. So far, the current of the commercially available FEA device is limited to -0.1 A/mm2. To reach higher currents, we explore the field-emission properties of pyramidal-shaped molybdenum FEAs based on the molding-technique. For high-current applications, the pyramidal tip with low-aspect ratio is advantageous over a conical/cylindrical one because of the higher thermal conductance and thermal spread. Here we present fabrication and characterization of pyramidal-shaped molybdenum FEAs with relatively small numbers of tips (1) to measure the maximum current I max per tip for single-gate devices, and (2) to explore the spatially- and energy-resolved photoemission in FEAs without gate electrodes.

In order to find electron sources with low intrinsic

The properties of the electron source define the ultimate limit of the beam quality in linear accelerators such as free electron lasers (FELs). The goal is to develop an electron gun delivering beam emittance lower than the current state of the art. Such a gun should reduce the cost and size of an x-ray FEL (XFEL). In this article we present two concepts of field emitter cathodes which could potentially produce low emittance beam. The first challenging parameter for such cathode is to emit peak current as high as 5 A. This is the minimum current requirement for the XFEL concept from Paul Scherrer Institut (http://leg.web.psi.ch). Maximum currents of 0.12 and 0.58 A have been reached, respectively, with field emitter arrays and single needle cathodes. Laser assisted field emission gave encouraging results to reach even higher peak current and to prebunch the beam.

In order to find electron sources with low intrinsic emittance ( 5.10A.m.rad), single tip field emitter as well as Field Emitter Arrays (FEAs) are investigated. By field emission very high current densities can be obtained (up to 10A.m) from extremely small source sizes. Illumination of such field emitting sources by laser pulses (photo-field emission) gives in addition the possibility to pre-bunch the emission to very short pulse lengths. Maximum peak currents, measured from single tips of ZrC with a typical apex radius around one micrometer are presented. Voltage pulses of two nanoseconds duration and up to 50 kilovolts amplitude lead to field emission currents of several hundreds of milliamperes. By combining these electrical pulses with laser pulses, peak currents of several amperes were extracted from the tip apex. This high current emission mode is different from field emission or photo-field emission and has many similarities with the so-called explosive electron emission.

In order to find electron sources with low thermal emittance, cathodes based on single tip field emitter are investigated. Maximum peak current, measured from single tip in ZrC with a typical apex radius around 1μm, are presented. Voltage pulses of 2ns duration and up to 50kV amplitude lead to field emission current up to 470mA from one ZrC tip. Combination of high applied electric field with laser illumination gives the possibility to modulate the emission with laser pulses. Nanoseconds current pulses have been emitted with laser pulses at 1064nm illuminating a ZrC tip under high-DC electric field. The dependence of photo-field emitted current with the applied voltage can be explained by the Schottky effect.

Today most of the X-rays Free-Electron Laser projects are based on state of the art RF guns, which aim at a nor- malized electron beam emittance close to 1 mm·mrad. In this paper we report on the progress made at PSI towards a hybrid DC + RF Low Emittance Gun (LEG) capable of producing a beam with an emittance below 0.1 mm·mrad. To reduce the intrinsic thermal emittance at the LEG cath- ode the electrons are extracted from nano-structured field- emitters. A gun test facility is under construction wherein after emission the beam is accelerated up to 500 keV in a diode before being injected and accelerated in a two- frequency 1.5-cell RF cavity. The fast acceleration in the diode configuration allows to minimize the emittance di- lution due to the strong space charge forces. The two- frequency RF structure is optimized to limit the emittance blow-up due to the non-linearity of the RF field.